Singlet and triplet excited state properties of natural chlorophylls and bacteriochlorophylls

Niedzwiedzki, Dariusz M.; Blankenship, Robert E.

doi:10.1007/s11120-010-9598-9

Cited by 119 publications

(128 citation statements)

References 37 publications

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“…These values are larger than those calculated from the spectral densities with the standard prefactor [65] in our previous paper [22]. Our MD/TDDFT calculations imply that the reorganization energies of the BChl d in the roll is larger than that in solvent (69 cm −1 ) [66]. This large reorganization energy can be a signature of a fast energy relaxation within Q y exciton states in the roll.…”

Section: A Spectral Densitiescontrasting

confidence: 58%

Theoretical characterization of excitation energy transfer in chlorosome light-harvesting antennae from green sulfur bacteria

et al. 2014

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We present a theoretical study of excitation dynamics in the chlorosome antenna complex of green photosynthetic bacteria based on a recently proposed model for the molecular assembly. Our model for the excitation energy transfer (EET) throughout the antenna combines a stochastic time propagation of the excitonic wave function with molecular dynamics simulations of the supramolecular structure, and electronic structure calculations of the excited states. We characterized the optical properties of the chlorosome with absorption, circular dichroism and fluorescence polarization anisotropy decay spectra. The simulation results for the excitation dynamics reveal a detailed picture of the EET in the chlorosome. Coherent energy transfer is significant only for the first 50 fs after the initial excitation, and the wavelike motion of the exciton is completely damped at 100 fs. Characteristic time constants of incoherent energy transfer, subsequently, vary from 1 ps to several tens of ps. We assign the time scales of the EET to specific physical processes by comparing our results with the data obtained from time-resolved spectroscopy experiments.

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Section: A Spectral Densitiescontrasting

confidence: 58%

Theoretical characterization of excitation energy transfer in chlorosome light-harvesting antennae from green sulfur bacteria

et al. 2014

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“…TRF measurements were carried out using the laser system and universal streak camera setup described in detail previously (52), exciting at 602 nm. The spectra were cleared from noise and globally fit using the program ASUfit (13).…”

Section: Methodsmentioning

confidence: 99%

“…In oxidizing conditions, the fast lifetime of the quenching pathway (60 ps) is thought to compete with the rate of energy transfer to the RC. This pathway effectively disappears in reducing conditions, allowing the pigments to fluoresce with lifetimes similar to that of monomeric BChl a (2 ns) (13). It was suggested that the quenching effect might be controlled by a modified aromatic amino acid (e.g., tyrosylquinone or trytophylquinone) that plays a role similar to that of the excitation-quenching quinones found in the chlorosome (12).…”

mentioning

confidence: 99%

Evidence for a cysteine-mediated mechanism of excitation energy regulation in a photosynthetic antenna complex

Orf

Saer

Niedzwiedzki

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Light-harvesting antenna complexes not only aid in the capture of solar energy for photosynthesis, but regulate the quantity of transferred energy as well. Light-harvesting regulation is important for protecting reaction center complexes from overexcitation, generation of reactive oxygen species, and metabolic overload. Usually, this regulation is controlled by the association of lightharvesting antennas with accessory quenchers such as carotenoids. One antenna complex, the Fenna-Matthews-Olson (FMO) antenna protein from green sulfur bacteria, completely lacks carotenoids and other known accessory quenchers. Nonetheless, the FMO protein is able to quench energy transfer in aerobic conditions effectively, indicating a previously unidentified type of regulatory mechanism. Through de novo sequencing MS, chemical modification, and mutagenesis, we have pinpointed the source of the quenching action to cysteine residues (Cys49 and Cys353) situated near two lowenergy bacteriochlorophylls in the FMO protein from Chlorobaculum tepidum. Removal of these cysteines (particularly removal of the completely conserved Cys353) through N-ethylmaleimide modification or mutagenesis to alanine abolishes the aerobic quenching effect. Electrochemical analysis and electron paramagnetic resonance spectra suggest that in aerobic conditions the cysteine thiols are converted to thiyl radicals which then are capable of quenching bacteriochlorophyll excited states through electron transfer photochemistry. This simple mechanism has implications for the design of bio-inspired light-harvesting antennas and the redesign of natural photosynthetic systems.photosynthesis | Fenna-Matthews-Olson protein | excitation quenching | thiyl radical | light-harvesting P hotosynthesis can be performed in the presence of oxygen (oxygenic photosynthesis, in which water is the electron source) or in its absence (anoxygenic photosynthesis, in which other reduced species such as sulfide are the electron sources) (1-3). Many bacteria performing anoxygenic photosynthesis contain type I reaction center (RC) protein complexes that use Fe-S clusters to transfer electrons to ferredoxin or related molecules after photoinduced charge separation (4-6). These Fe-S clusters are easily damaged by molecular oxygen. Therefore, anoxygenic phototrophs must use a pathway either to remove oxygen or to reduce the rate of photosynthesis whenever oxygen is encountered (1, 5).Phototrophic members of the bacterial phylum Chlorobi (green sulfur bacteria, GSBs) are anoxygenic phototrophs that contain such a type I RC. They also contain two peripheral antenna complexes that aid in regulating light absorption and energy transfer: the chlorosome and the homotrimeric Fenna-Matthews-Olson (FMO) protein complex. When oxygen is encountered, the bacteria are able to decrease the output of photosynthesis. This process involves creating trapping sites in the antenna complexes where de-excitation processes outcompete the rate of energy transfer to the RC, preventing RC damage. This process is well un...

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“…As light harvesters, carotenoids transfer the absorbed excited state energy to (bacterio)chlorophylls ((B)Chl); this excitation energy is eventually trapped by a reaction centre pigment -protein complex and converted into an electrical potential [19,20]. They also act as protective molecules against the photobleaching of photosynthetic organisms by quenching (B)Chl triplet states [21,22], which prevents the (B)Chlsensitized formation of singlet state oxygen [23][24][25][26][27][28][29], by scavenging singlet oxygen directly [8,30] or by quenching (B)Chl singlet states [31 -33]. Carotenoids have also been reported to stabilize protein structures, because many photosynthetic pigment -protein complexes do not fold properly without these molecules [34 -36].…”

Section: Introductionmentioning

confidence: 99%

Electronic and vibrational properties of carotenoids: from in vitro to in vivo

Llansola-Portolés¹,

Pascal²,

Robert³

2017

J. R. Soc. Interface.

103

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Carotenoids are among the most important organic compounds present in Nature and play several essential roles in biology. Their configuration is responsible for their specific photophysical properties, which can be tailored by changes in their molecular structure and in the surrounding environment. In this review, we give a general description of the main electronic and vibrational properties of carotenoids. In the first part, we describe how the electronic and vibrational properties are related to the molecular configuration of carotenoids. We show how modifications to their configuration, as well as the addition of functional groups, can affect the length of the conjugated chain. We describe the concept of effective conjugation length, and its relationship to the S 0 ! S 2 electronic transition, the decay rate of the S 1 energetic level and the frequency of the n 1 Raman band. We then consider the dependence of these properties on extrinsic parameters such as the polarizability of their environment, and how this information (S 0 ! S 2 electronic transition, n 1 band position, effective conjugation length and polarizability of the environment) can be represented on a single graph. In the second part of the review, we use a number of specific examples to show that the relationships can be used to disentangle the different mechanisms tuning the functional properties of protein-bound carotenoids.

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Singlet and triplet excited state properties of natural chlorophylls and bacteriochlorophylls

Cited by 119 publications

References 37 publications

Theoretical characterization of excitation energy transfer in chlorosome light-harvesting antennae from green sulfur bacteria

Theoretical characterization of excitation energy transfer in chlorosome light-harvesting antennae from green sulfur bacteria

Evidence for a cysteine-mediated mechanism of excitation energy regulation in a photosynthetic antenna complex

Electronic and vibrational properties of carotenoids: from in vitro to in vivo

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